The invention relates to setting register on a multicolor printing machine having color printing units allocated to various printing inks and having image cylinders, equipment for producing images, in particular electrostatic latent images, on the image cylinders, a carrier for printing substrates and image transfer points for the transfer of the color separations from the color printing units to the printing substrates, a time independent allocation of the image productions on the image cylinders being carried out in order to achieve coincidence of register of the color separations in the print.
The invention further relates to apparatus for setting register in accordance with the above-described method on a multicolor printing machine having color printing units allocated to various printing inks and having image cylinders, equipment for producing images, in particular electrostatic latent images, on the image cylinders, a carrier for printing substrates and image transfer points for the transfer of the color separations from the color printing units to printing substrates, sensors for measuring position, and at least one setting device for allocating the positions of the image production points on the image cylinders to the printing substrates in order to achieve coincidence of register of the color separations in the print. Furthermore, the invention relates to an appropriately equipped multicolor printing machine.
Printing color illustrations, in particular color images, is carried out by a number of color separations being printed over one another. These are generally the colors yellow, magenta and cyan, as well as black. If required, special colors are added. By overprinting these colors, all color compositions can be achieved, the quality of the prints depending significantly on the in-register overprinting of the color separations. In conventional, non-automated printing processes, the printing plates are corrected by means of test prints and register marks printed at the same time as these until exact overprinting, that is to say, maintenance of register in the print, is achieved.
In digital printing processes, the image cylinders are written with image points by image production equipment in each case, by electrostatic charges being generated and these being provided with adherent colored pigments. The colored pigments are then transferred to a printing substrate. In digital printing processes, maintenance of register can be achieved by the image production equipment being controlled appropriately. Since the setting of an image is carried out anew for each print, it is not necessary, as in conventional printing processes, for a one-off setting to be made, but presetting and control can be provided, which performs corrections for each individual print. Of course, this does not apply only to the application of electrostatic latent images but also to all other printing processes in which image points are applied by a digital control system.
For an electrostatic printing process of the type mentioned at the beginning, U.S. Pat. No. 5,287,162 has, therefore, proposed to print register marks preferably onto the carrier for the printing substrates and to detect these by an apparatus. Here, the times, which the register marks need to pass from production by the image production equipment to a detection point are determined. These times are then used to determine the instants at which the image production equipment perform the image setting on the individual image cylinders, in order to achieve the maintenance of register after the images have been transferred to a printing substrate.
Since achieving coincidence with respect to image setting on the image cylinders leads to inaccuracies if there are differences in speed relating to the surfaces of the image cylinders, U.S. Pat. No. 5,287,162 has proposed to record calibration tables with times which are allocated to various angular positions of the image cylinders, in order, with the aid of these calibration values, to eliminate regularly occurring fluctuationsxe2x80x94which are mostly caused by unroundnesses of the cylindersxe2x80x94and in this way to make the corrections for each individual print.
Since the maintenance of register required for high printing qualities requires extremely high precision, such calibration tables, in which time values are set, are inadequate, however. It is not possible to take into account irregularities, which are reflected in differences in time intervals, which cannot be allocated to rotational angles of the image cylinders. Nor is the latter helped either by a proposal in U.S. Pat. No. 5,287,162 to draw up the calibration tables again and again since by this means only the long-term and slow drift of the values can be taken into account, but no short-term differences that cannot be allocated to angular positions of the image cylinders.
A typical example of such irregularities, which are not reflected in differences between time intervals, are fluctuations in the speed of the drive system, since the allocation of the same to specific rotary angles of the image cylinders or other cylinders is not possible, since these fluctuations do not exhibit any synchronism with the angular positions of the image cylinders or other cylinders. Regulation by a calibration table of the type proposed with time values, which is allocated to the rotary angles of the image cylinders, would, thus, rather produce errors than eliminate errors. Thus, in investigations it has been determined, for example, that the poles of the electric drive motors occur as items which cause frequency-type speed fluctuations of the drive, which, because of the different transmission distances, also do not exhibit any synchronous occurrence on all the image cylinders and, therefore, lead to time/position differences on the individual image cylinders. These frequency-type fluctuations are sufficient to cause faults in the register setting. Faults of this type can occur as early as at the start of the image or can make themselves noticeable in the image quality as faults in subareas of images, for example, as register inaccuracies like transverse stripes. Since such frequency-like fluctuations of the drive system are superimposed on other faults, such as unroundnesses of image cylinders, it is no longer possible to draw up calibration tables for correction with a tolerable outlay. These tables could no longer be oriented to the angular positions of the image cylinders or other cylinders for one revolution or for a comprehensible sequence of revolutions, but it would be necessaryxe2x80x94if this is at all possible as a result of the complexityxe2x80x94for a curve of calibration values relating to complex machine configurations as far as the occurrence of a repetition situation to be determined. However, drawing up correction values over relatively long time periods in this way is, in turn, opposed by the fact that there are also further causes of faults, such as irregularities in the guidance of the carrier and primarily also long-term changes such as temperature changes, the change in mechanical stresses in the machine, changes in the type of paper, the amount of toner, and so on. Such a xe2x80x9ccolorful mixturexe2x80x9d of faults, which change in the short term and behave synchronously with respect to the angular positions of cylinders, with faults, which likewise change in the short term but not synchronously with the angular positions, and long-term asynchronous changes, oppose the achievement of high precision by a correction with the aid of the proposed calibration tables with time values.
The invention is, therefore, based on the object of configuring a method, and an apparatus in such a way that high precision of the register setting can be achieved with a tolerable outlay, in particular as far as possible without reject prints. At the same time, both the rapid and most exact possible presetting, as well as a continuous rapid correction of the register setting, is to be made possible.
According to the invention, the object is achieved in that a time-independent allocation of the positions of the image productions on the image cylinders to the printing substrates is carried out for at least one defined area of all the color separations. Further, the object is achieved by the sensors being designed to measure the positions of elements that carry images and substrates, and by at least one setting device being such that it allocates the positions of the image productions on the image cylinders to the printing substrates with regard to at least one defined area of the color separations in a time-independent manner.
With regard to the apparatus, according to the invention, the object is achieved by the sensors being designed to measure the positions of elements that carry images and substrates, and by at least one setting device being designed in such a way that it allocates the positions of the image productions on the image cylinders to the printing substrates with regard to at least one defined area of the color separations in a time-independent manner.
The invention is based on the observation that the presetting and/or regulation of a register, in which recorded times are placed in a relationship with one another, leads to an increase in the complexity of the superimposition of faults, since faults arising from the determination of positions by times are added to the actual register fault causes. This addition of a further fault cause is, therefore, problematical for counter measures, since the last-mentioned faults are faults, which occur in the short term and behave asynchronously in relation to the angular positions of the image cylinders.
The invention is further based on the finding that if, instead of the times, the positions are placed directly in relationship with one another, the faults which do not behave synchronously in relation to the angular positions of the cylinders, for the most part, no longer occur, since they arise from the time-position allocation. They, therefore, do not have any influence on the setting of the register if a direct mutual allocation of positions is made the basis for control or regulation. Such direct position allocations can, for example, be designed in such a way that distances or angular positions are allocated to one another. By the measure according to the invention, the frequency-type fluctuations of the drive system or similar fault sources no longer have any influence on the register setting, since the positions are measured directly and no longer by the circuitous route via times.
The invention achieves the situation where the short-term fluctuations which still remain are repeated essentially synchronously with the angular positions of the image cylinders or other cylinders, as referred to one revolution or a short sequence of revolutions. It is, therefore, also possible to draw up calibration tables for the image production in each color printing unit which apply for a specific time duration. Long-term changes can then be taken into account during printing by calibration tables, which are based on the measurement of positions being renewed again and again. This renewal of calibration tables corrects slow drift. The calibration tables can be drawn up virtually without errors only by means of the measure of the invention, since the short-term faults that behave asynchronously in relation to the angular positions of the image cylinders are, for the most part, avoided and no longer influence the setting of the register based on position allocation. However, the invention is, of course, riot restricted to calibration tables. Calibration tables are only one configuration, but as a result of the invention, these can be used for the first time for precision setting.
The invention makes it possible to measure and to eliminate virtually all fault sources belonging to elements that carry images or printing substrates, since the short-term faults are for the most part reduced to the faults which occur synchronously with angular positions and which, in relation to a repetition per revolution, permit longer-term faults to be separated from the latter. In this case, it does not matter whether the faults, which still remain, are based on the diameter faults or imbalances of image cylinders or further cylinders transferring the images. It is also possible for transfer faults caused by the behavior of elastic material, such as that of cylinder covers, by different contact forces or by differences in mechanical stresses of carriers for printing substrates or the pressure setting of an impression roll which is used for the image transfer to a substrate, to be measured and eliminated, since these faults can be allocated to the angular positions of the respective components that carry images or substrates in a synchronous way, and can therefore be corrected by calibration tables to be drawn up in each case.
There are two possibilities for determining the correction values for the image production. A calibration table can be provided which contains a cycle as far as the occurrence of a repetition. A cycle of this kind can be a revolution or a sequence of revolutions. However, it would be conceivable to draw up calibration tables for other elements that carry images or substrates, relating to all the positions up to the repetition of the same, in order to perform the setting of images on the image cylinder by means of a calculation from the values of all the calibration tables, with the elimination of all the differences which occur in terms of their effect on the positions to be coordinated with one another. By continual determination of the positions during printing, it is also possible for slow drift, for example, as a result of temperature differences and stresses in the machine, to be detected and eliminated. Of course, it is also possible to detect and eliminate faults, which occur as a result of changes in the printing substrate used, changes in the images or in the toner or as a result of other influences.
The allocation of positions according to the invention is possible with or without a calibration table and in various ways. Thus, for example, angular positions or also distances of surfaces of elements that carry images and substrates can be allocated to one another. A combination of angular positions and distances is also possible. One of the elements is expediently taken as a reference. One configuration of the method, therefore, proposes that, for the color separations, in each case the at least one defined area on the image cylinders is produced in relation to predefined positions of the carrier. Another proposal is for at least one defined area of the color separation from a reference printing unit to be assigned to at least one defined area of the color separations from the other color printing units in each case, and for an allocation to a position of the carrier then to be made.
With regard to the apparatus, one proposal is that the at least one setting device be such that it initiates the production of at least one defined area of all the color separations on the respective image cylinders to predefined positions of the carrier. Depending on the aforementioned chosen method, the setting device can also have a different appropriate design.
For the position allocations of the carrier, one proposal provides for the angular positions of the drive roller of the carrier to be used. In addition, the angular positions of the image cylinders can be used for their position allocations. One further possibility is to use the distances of the surface of the carrier for the position allocations of the carrier. In a corresponding way, the distances of the surfaces of the image cylinders can be used for the position allocations of the image cylinder.
With regard to the apparatus, for the use of the angular positions to allocate the positions, it is proposed that at least one sensor be an angular position transmitter, one sensor being proposed for each element whose angular positions are to be measured. Furthermore, at least one setting device must be for the allocation of angular positions. It is additionally possible for at least one sensor for detecting a circularity error to be provided, as well as at least one setting device, which determines the positions from angular positions and circularity errors. The purpose is that it is the actual distances covered by the defined areas of the color separations, which are concerned, and circularity errors lead to the angular positions not being an exact measure of this. An appropriate correction can be made by the proposed detection of the circularity errors, the aforementioned faults being avoided and, nevertheless, the relatively simple measurement of position and allocation of position by the angular positions being possible.
For determining a position by distances, it is proposed that at least one sensor measure distances, one sensor being proposed for each element whose distances are to be measured. In this case, one configuration can have sensors to detect distance marks and the latter being applied to the appropriate surfaces. It is then additionally necessary for at least one setting device to be for the allocation of distances.
For machines, which have additional image transfer cylinders, which are arranged between the image cylinders and the carrier, it is proposed that the positions of image transfer cylinders be included in the position allocations as well. For the allocations of the positions of the image transfer cylinders, their angular positions can be used, or it is possible for the distances of the surfaces of the image transfer cylinders to be used for the allocation of the positions of the same. With regard to the apparatus, in each case at least one sensor must then be provided to measure the positions of the image transfer cylinders, and these positions must be transmitted to at least one setting device for calculating the allocation. The sensor used here can also be both an angular position transmitter, if necessary combined with a sensor for detecting a circularity error, or it is possible for a sensor for measuring distances to be provided.
One configuration of the method according to the invention provides for the mutually assigned defined areas of the color separations to be the image starts. In order to perform this allocation, at least one setting device is such that it predefines the positions of the carrier at which the beginning of image setting on the image cylinders takes place.
In order to achieve exact maintenance of register of the images over all image areas, provision is made for the mutually allocated defined areas to be the areas of the color separations into which the image areas are subdivided. The areas of the color separations can be individual lines of image points or a number of lines of image points of the color separations. In the first case, the lines of image points are allocated to the color separations, in the last-mentioned case, the number of lines of image points is allocated, in order to achieve the coincidence of register. A configuration, which is expedient for the allocation of angular positions, provides for the number of lines of image points of an area to result from the allocation to fixed angular intervals on the image cylinders. Apart from the positions in the direction of movement, however, the lateral position of the areas can also be determined and set. It is preferable also for faults relating to the lateral extent of the areas to be determined and corrected.
In order to perform these settings and corrections, with regard to the method, at least one setting device is such that it predefines the positions of the carrier at which the setting of images on the image cylinders is carried out with the areas into which the image area is subdivided. Here, the areas can be strips, which extend over the image area transversely with respect to the direction of movement. However, for a lateral setting, these strips can also be subdivided transversely again, or a lateral setting is performed which relates directly to the distances between the image points.
A particularly expedient configuration of the invention provides for the positions to be determined by register marks. Determining the positions in this way can be carried out both before carrying out a print, in order to perform the setting, and while a print is being made, in order to carry out corrections to the values. The register marks preferably have elements arranged in the transport direction and spaced apart in a predefined way, the distances being measured. Register marks of this type are printed by each color printing unit, it being possible for the individual elements printed by individual color printing units to form rows or for a number of elements spaced apart to be printed one after another by individual color printing units. The register marks can be ongoing or in groups, it being possible for these again to have defined spacings from one another. As a result, the aforementioned positions can be measured and allocated. If the positions should be measured before printing, it is expedient to print the register marks directly onto the carrier and to remove them again after the determination of position. During printing, it is expedient for the register marks to be printed in the space on the carrier not covered by printing substrates. However, it is also possible to print the register marks on paper, which can be a test sheet, or it is possible for this purpose to use image-free edges of the printing substrates. With regard to the apparatus, at least one sensor can be provided for detecting register marks. Said sensor is expediently designed in such a way that it measures the distances between elements of the register marks which are spaced apart in a predefined way.
Following the measurement of the data for all the color printing units, the deviations of the actual values from the desired values for the image starts are expediently separated from the deviations of the actual values from the desired values for the other areas into which the image areas are subdivided, by an appropriately programmed computing device by an analysis of the measured positions. The values are then given to setting devices for the image starts and to setting devices for the defined areas of the color separations. These setting devices are equipped with machine-specific nominal values, being such that, before the start of printing, they take into account correction values for determining the positions on the image cylinders, if the machine is one in which the image cylinders transfer the image directly to the substrates, then, in this case, the distance from the image production points as far as the image transfer points to the image cylinders is decisive. If the machine is one which has image transfer cylinders, then the distance from the image transfer point between image cylinder and image transfer cylinder as far as the image transfer point to the substrate is added. Furthermore, the setting devices can be such that, after the start of printing, they take into account correction values for the positions.
It is preferable if, following the measurement of the positions for the image starts on the individual image cylinders, these positions for the image production of the other defined areas on the individual image cylinders are measured such that they are linked with the first and used in this sequence for control or regulation. In this way, firstly the register of the position of the beginning of the color separations and then the position for individual image areas are set.
It is advantageous if, in the case of the measured values, noise, that is to say, fluctuations that occur in the very short term, are eliminated for the evaluation (in order to avoid control instability). In addition, the other fluctuations in the measured position values, which, with regard to their order of magnitude and repetition, can be allocated to a repeatable position of a cylinder, are separated from longer-term fluctuations. The fluctuations in the measured position values which, with regard to their order of magnitude and repetition, can be allocated to a repeatable position of an image cylinder, are entered into at least one calibration table for this image cylinder and used for the fault-compensating control of the positions of the image production points for producing the images of the respective image cylinder. The calibration tables are expediently drawn up both for the image starts of the color separations and for the defined areas of the color separations.
In addition, for the further elements that carry images or substrates, deviations which can be allocated to their repeatable positions in a movement cycle of the actual positions from the desired positions are measured and included in the calculation of the image production points in order to eliminate these deviations. These are, for example, the image transfer cylinders in the case of appropriately configured machines. In addition, calibration tables can be drawn up for such elements that carry images or substrates, in order then to include all the calibration tables in the calculation of the positions of the image production points. Longer-term fluctuations which cannot be allocated to repeatable positions of a movement cycle are taken into account by ongoing renewal of the calibration tables. The calibration tables are corrected before each print job, but it is also possible to correct them continuously during printing. With regard to the apparatus, such calibration tables can be available in appropriate files for controlling the setting devices. Such files are initially available as machine-specific nominal values, and are taken into account by setting devices, even before printing is started, as correction values for the positions of the image productions on the image cylinders. Likewise, such correction values can be taken into account for the positions on the image transfer cylinders, the latter correction values likewise being implemented via a correction of the image productions on the image cylinders in order to achieve maintenance of register. A print is then made, register marks expediently being printed first before the print job is carried out and their position being measured, in order to take into account the correction values determined in this way for determining the positions of the image productions. After that, register marks can also be printed at the same time during the processing of a print job, in order to detect changes and to be able to make further corrections.
Boundary conditions which have an influence on the register should be taken into account in as timely a manner as possible by corrections to the position values. For good print quality and the avoidance of rejects, it is, therefore, desirable to include such changes as early as possible in the calculation of the position values. For this reason, it is proposed that errors in the measured position values which occur in the longer term and cannot be allocated, by their repetition, to a repeatable position of an element that carries an image or substrate, be taken into account by detecting and including the influencing variables which cause them in the correction for the register control. This detection and inclusion of the influencing variables in the correction is expediently carried out on the basis of stored values from experience. For this purpose, the setting devices are such that, before the start of printing, they take into account correction values for the measurement of the positions which can be allocated to detectable influencing variables, and are available as at least one selectable files with values from experience. The choice of such a file can be made via an input device, that is to say activated by a manual input, or it is also possible for the choice to be made by a setting device on the basis of at least one measurement of at least one influencing variable, that is to say the inclusion of a file for correction is activated by a measurement of the influencing variable. Furthermore, an influencing variable can be measured in terms of its effect on the register, and a correction to the image production can be made in accordance with these deviations.
There are numerous influencing variables of this type, which are related to the print job or environmental influences, which one, therefore, knows or which can be measured. One example of this is the temperature at specific locations in the printing machine. In order to take this into account, it is proposed that at least one temperature sensor be arranged in the printing machine, and the measured temperatures be made the basis for a correction. Mechanical stresses on specific machine parts of the printing machine can also be of influence for the maintenance of register. It is, therefore, proposed, that this influencing variable be detected by arranging at least one stress sensor, and that the measured values be made the basis for a correction.
A further influencing variable is the paper grade, in this case the values from experience for the respective paper grade are stored and, when a new paper grade is fed in, reference is made back to the appropriate file. The toner profile of the image to be printed also has an influence, it being possible to take this into account by the color printing machine being equipped with a device for measuring a toner profile, or the latter being measured in advance and input into the controller. It is then expedient for values from experience for different toner profiles to be available.
Since, during printing, displacement of a substrate on the carrier can occur, it is also possible to detect this and to correct the image productions in order to compensate for such a displacement. With regard to the apparatus, it is proposed that a sensor be provided for detecting a displacement of a substrate on the carrier, and the setting devices be such that the positions of the image productions be corrected in order to compensate for this displacement.
Further values from experience can be available for various image widths or for various paper widths, in order to carry out the appropriate corrections. It is also possible for values from experience for changes in the substrate dimensions following image setting on one side to be taken into account in order that the image size of the verso print corresponds to the image size of the recto print. As a result, changes in the substrate dimensions as a result of flexure of the same during printing, as a result of the application of color or as a result of the fixing of the colors by fusing can be taken into account.
By values from experience, the retroactive influence of the state preceding a change can also be taken into account. Such a retroactive effect occurs, for example, in the case of a paper grade change when the image cylinder is already having the image for the new paper grade set while the preceding image is still being printed on the previous paper grade.
In addition to the aforementioned corrections, however, others are also conceivable. Provision can, thus, be made for fluctuations in the position values which, with regard to their repetition, cannot be allocated to the angular position of an image cylinder but occur repeatedly and regularly, are entered into separate calibration tables and used for the fault-compensating control of the device for producing the images on the respective image cylinder. For example, fluctuations in the position values which, with regard to their repetition, cannot be allocated to the position of the carrier for the printing substrates, can be corrected in accordance with the position of the carrier, this correction being added to the corrections of the position of values which can be allocated to the position of the image cylinders, and being taken into account for the position at which the color separations are produced on the image cylinders. Of course, fluctuations in the position values can also be avoided by ruling out their causes.
For example, with regard to the carrier, provision can be made for its periodically occurring irregularities to be measured in advance and set into the calculation, or it is also possible for the circumference of the drive roller of the carrier to be dimensioned, in relation to the spacing between the image transfer points of the color printing units, in such a way that the allocation of the angular positions of the drive roller to the image cylinders repeats. This may be implemented by it being possible for the circumference of the drive roller of the carrier to be inserted into the distance between the image transfer points of the color printing units. In this case, it may be possible to insert it as a half or preferably as a whole number. A development of this type is primarily expedient when the drive roller drives the image cylinders via the carrier and possibly via the image transfer cylinders, since irregularities resulting from unroundness of the drive roller then act simultaneously on all the color printing units and can no longer influence the register setting. The aforementioned configuration is also expedient when the distances of the carrier are measured by means of an angular position transmitter belonging to the drive roller, since the differences in speed of the carrier which are not registered by the angular position transmitter and result from unroundnesses of the drive roller no longer have to be measured either, since their influence has already been ruled out in the aforementioned way.
It is often the case that a completely exact determination of the position values on the basis of the measured data is not possible. For example, measurements usually have a certain scatter, they can exhibit differences over the image width, or short-term fluctuations arise as a result of oscillations. For such cases, it is proposed that, within a tolerable bandwidth of measured distance values, the correction is set to a central range. For example, in the case of various position values transverse to the transport direction, an average value can be set. Here, it is possible that, in order to calculate the average value, for the measured deviations to be weighted, quadratic weighting being proposed as an example. Other weightings are, of course, possible, being made in view of the fact that the influence of the deviations on the image quality is at a minimum. Expediently, the values from the color printing units, which lie in the central range, are brought into alignment with the value from a reference printing unit that lies in the central range.
With regard to the calculation of the positions of the image cylinder in which the images are produced, it is proposed that the arrival of a printing substrate be detected and then the positions for the respective beginning of setting the image on the image cylinders being determined as positions, for example, as distances of the carrier beginning from a detection point for printing substrates. These calculations are initially made on the basis of the values previously determined and input, subsequent corrections being made by at least one device determining the corrections to the positions necessary on the basis of measuring the positions during printing, and transmitting these to the setting devices to be implemented.
Since an analysis of the measured values can be made, in a manner already proposed, to the effect that the differences in position for the image starts are separated from the differences in position for the remaining areas into which the image areas are subdivided, with regard to the apparatus for setting register, it is proposed that at least one device for determining the corrections for the image starts be connected to the sensor for measuring the positions of the carrier and to the sensor for detecting the register marks. In this way, the device for determining the corrections is given the data relating to the deviations of the positions of the register marks from the previously calculated positions, and as a result can calculate and initiate the corrections.
In addition, it is proposed that a device for determining the corrections for the areas of the color separations into which the image areas are subdivided be connected to the sensor for measuring the positions of the carrier and to the sensor for detecting the register marks. In this way, the differences between the precalculated positions from the positions registered by the register marks can also be measured for the areas of the color separations into which the image areas are subdivided, and the corrections can be calculated.
The starting signal for the image starts is linked with the start of the other areas into which the image areas are subdivided, by a device for the output of starting signals for the image starts simultaneously giving starting signals to devices for the allocation of the areas into which the image area is subdivided, this device being connected to the sensor for measuring the positions of the image cylinders and allocating to these positions the areas into which the image area is subdivided.
In order to have sufficient time available for calculating the positions needed for precise register setting, it is further proposed that a sensor for detecting a printing substrate which is fed to the printing machine be arranged on the distance of the printing substrates to the printing machine and be connected to the setting devices, the calculation of the mutual allocation of the positions of the image production points being started when a printing substrate is detected. Since this sensor on the distance of the printing substrates to the printing machine cannot detect their leading edge exactly enough, it is also proposed that a sensor for the accurate detection of leading edges of printing substrates be arranged on the carrier and connected to devices which calculate the distances which the printing substrate covers from this sensor as far as the positions of the beginning of the respective image setting process, in order then to initiate the beginning of the image setting in the correct position. However, it is of course also possible for a sensor, which is arranged on the carrier to perform both functions, if an adequate distance is available.
In addition, the multicolor printing machine, proposed in accordance with the invention, can have all of the above-described apparatus features and can be such that it can operate in accordance with all the above-described method features.